Residential and light commercial construction generally use wood lumber as the primary building material for studs, plates, joists, headers and trusses. However, wood lumber construction has problems. The rapidly rising cost of raw wood supplies has in effect substantially raised the cost of these members. Further, the quality of available framing lumber continues to decline. Finally, wood is flammable and susceptible to insects and rot.
Due to these problems, many builders have been switching to light gauge steel framing. The costs between using wood or steel framing is getting closer. In January 1990, the cost of framing lumber was about $225 per thousand board feet, peaking to highs of $500 in both January, 1993 and January 1994. Since June 1995, the framing lumber composite price has been rising from $300 per thousand board feet. Estimates from the AISI and NAHB Research Center state at a framing lumber cost of $340 to $385, there would be no difference between the cost of framing a house in steel as compared in wood. Thus, the break-even point between wood and steel framing is at about $360 per thousand board feet of framing lumber, and the lumber price has exceeded that point several times in recent years by as much as 40% giving steel a competitive advantage.
Recycling has additionally helped the cost of steel to remain on a stable or downward trend. Steel costs have varied little in recent years. Traditionally variations can be correlated to steel demand by the automobile industry, when demand is high, steel usually increases slightly in price. Consequently, the use of metal framing in residential and light commercial construction is increasing, a trend recognized and encouraged by the American Iron and Steel Institute (AISI).
Steel studs, tracks and trusses are commonly manufactured in industry by companies such as Deitrich, Unimast, Alpine, Tri-Chord, HL Stud, Truswall Systems, Techbuilt, Knudson, John McDonald, and MiTek.
A problem with steel framing is its high thermal conductivity, leading to thermal bridging, xe2x80x9cghostingxe2x80x9d, and greater potential for water vapor condensation on interior wall surfaces. xe2x80x9cGhostingxe2x80x9d is when an unsightly streak of dust accumulates on the interior wallboard, where the steel studs lie behind, due to an acceleration of dust particles toward the colder surface. Another problem of using steel framing is the increased energy use for space conditioning (heating and cooling). Metal used for exterior framing members allows greater conduction heat transfer between the outside and inside surfaces of a wall, roof or floor. In colder climates, this increased conduction can cause condensation in interior surfaces, contributing to material degradation and mold and mildew growth. Metal framing also decreases the effectiveness of insulation installed in the cavity between the metal framing due to increased three-dimension thermal short circuiting effects. Higher sound transmission is another disadvantage of metal framing since sound conductivity is greater in metal than in wood. Electricians have more difficulty working with steel framing for running wiring since its more difficult to cut holes in steel than in wood, and grommets or conduits must be used to protect the wire.
U.S. Pat. No. 5,768,849 to Blazevic describes a xe2x80x9ccomposite structural postxe2x80x9d, title, having L-shaped metal members on sides of stud members, FIG. 3. However, L-shaped legs are directly connected to the side edges of the wood stud base, and are not structurally wrapped about side edges of the wood stud bases. The orientation of the L shaped legs would not adequately increase the thermal resistance over single wood material stud members, nor have a greater axial load capability over single wood material stud members, nor substantially reduce interior condensation and ghosting. The embodiments covering using cap shaped metal members in FIGS. 6, 6A, 7 and 7A are limited to using only the metal cap shapes in a longitudinal position as corner posts, and also would not adequately increase the thermal resistance over single wood material stud members, nor substantially reduce interior condensation and ghosting.
U.S. Pat. No. 5,285,615 to Gilmour describes a thermal metallic building stud. However, the Gilmour member is entirely formed from metal. In Gilmour, the thermal conductivity is only partially reduced by having raised dimples on the ends contacting other building materials.
U.S. Pat. No. 4,466,225 to Hovind describes a xe2x80x9cstud extendersxe2x80x9d, title, that is limited to converting a xe2x80x9c2xc3x974. . . into a 2xc3x976xe2x80x9d, abstract. However, Hovind is limited to putting their metal side xe2x80x9cextenderxe2x80x9d on one side of a xe2x80x9c2xc3x974xe2x80x9d, and thus would not adequately increase the thermal resistance over single wood material stud members, nor have a greater axial load capacity over single wood material stud members, nor substantially reduce interior condensation and ghosting.
U.S. Pat. No. 3,960,637 to Ostrow describes impractical metal and wood composites. Ostrow requires each end flange have tapered channels, the end flanges being formed from extruded aluminum, molded plastic and fiberglass. Ends of the vertical wood web must be fit and pressed into a tapered channel. Besides the difficulty of aligning these parts together, other inherent problems exist. Extruding the channel flanges from aluminum or using molds, cuts and rolling to create the channelled plastic and fiberglass end flanges is expensive to manufacture. To stabilize the structures, Ostrow describes additional labor and manufacturing costs of gluing members together and sandwiching mounting blocks on the outsides of each channel.
Other metal and wood framing member patents of related but less significant interest include: U.S. Pat. No. 5,452,556 to Taylor: U.S. Pat. No. 5,440,848 to Deffet; U.S. Pat. No. 5,072,547 to DiFazio: U.S. Pat. No. 5,024,039 to Karhumaki: U.S. Pat. No. 4,875,316 to Johnston: U.S. Pat. No. 4,301,635 to Neufeld: U.S. Pat. No. 4,274,241 to Lindal: U.S. Pat. No. 4,031,686 to Sanford: U.S. Pat. No. 3,566,569 to Coke et al.: U.S. Pat. No. 3,531,901 to Meechan: U.S. Pat. No. 3,310,324 to Boden.
The first objective of the present invention is to provide metal and wood composite wall stud that increases the total thermal resistance of a typical steel framed insulated wall section by some 43 percent and would eliminate condensation and xe2x80x9cghostingxe2x80x9d for all but the coldest regions of the United States.
The second object of this invention is to provide metal and wood composite framing combinations that achieve a resource efficient and economic construction framing member. Metal is used for its high strength, and potentially lower cost and resource efficiency through recycling. Wood is used primarily for its lower thermal conductivity and for its availability as a renewable resource, and for its workability.
The third object of this invention is to provide metal and wood composite framing members that allow electricians to be able to route wires through walls in the same way they are accustomed to doing with solid framing lumber.
The fourth object of this invention is to provide metal and wood composite framing members that would be easy to manufacture.
The fifth object of this invention is to provide metal and wood composite framing members that have low sound conductivity compared to prior art steel framing members.
The sixth object of this invention is to provide metal and wood composite framing members that have reduced effects from flammability compared to all wood members.
The invention includes J-shaped, P-shaped, L-shaped, triangular shaped cross-sectional metal forms connected by a wood midsection, whereby the wood is fastened to the metal by machine pressing of the metal to wood, similar to the common truss plate, or by nails, staples, screws, or other mechanical fastening means, or by adhesive glue. The outward faces of the metal members can be pre-formed with longitudinal ridges such that the contact surface area to applied sheathings is reduced by about 90%.
Metal and wood composites are used to create framing members (studs and tracks, joists and bands, headers, rafters, and the like) for light-weight construction. Metal is utilized for its high strength, resistance to rot and insects, cost stability and potentially lower cost through recycling. Wood is used primarily for its lower thermal conductivity, and availability. The metal components form the primary structure while wood, either solid or other engineered wood, provides some structure and a thermal break.
Metal and wood composite framing members can be used in place of conventional wood framing members such as: 2xc3x974 and 2xc3x976 wall studs, and 2xc3x978, 2xc3x9710, 2xc3x9712 and other dimensions of roof rafters, floor joists and headers. The novel framing members can be used to replace conventional light-gauge steel framing to reduce thermal transmittance and sound transmission.